Abstract
Fluoroaromatic scaffolds pose a challenge to lithiation due to low stability of lithiated intermediates. Here we apply trans‐metal‐trapping (TMT) to a series of key fluorinated aromatics. In TMT, LiTMP performs the metalation, while an organometallic trap intercepts the emergent carbanion. This study contrasts the trapping abilities of iBu2AlTMP and Ga(CH2SiMe3)3, structurally mapping their TMT reactions and probing relative stabilities of metalated fluoroaromatic intermediates by NMR studies. Results show the installed Al−C(aryl) bonds are more prone to decomposition by benzyne formation and Li‐F liberation, than the Ga−C(aryl) species. The latter are thus better for onward reactivity as demonstrated in cross‐coupling reactions with benzoyl chloride that produce ketones.
Highlights
Fluoroaromatic scaffolds pose a challenge to lithiation due to low stability of lithiated intermediates
Fluorinated aromatic compounds represent a special challenge to organolithium reagents on account of the instability of metalated intermediates.[3]
This point and the profound complexity involved are exemplified in Schlossers classic report of multiple hydrogen/lithium interconversions induced by lithiation of 1,3,5-trifluorobenzene.[4]
Summary
Fluoroaromatic scaffolds pose a challenge to lithiation due to low stability of lithiated intermediates. In TMT, LiTMP performs the metalation, while an organometallic trap intercepts the emergent carbanion.
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